Definition

A source is a text (sometimes oral presentation, audio recording, video recording) from which (genealogical) information is derived.

Scientifically, one will make 3 distinctions:

Primary source : text which is a firsthand written evidence of history, made at the time of the event by someone who has seen it happen. Eg: diaries, certificates, newspapers, ...

Secondary source : Written accounts of history based upon the evidence from primary sources and other secondary sources, offering commentary and analysis. Eg: history books, genealogical publications,...